Ceramic discharge lamp operable in air without an outer glass envelope

ABSTRACT

A ceramic discharge lamp operable in air without a conventional sealed outer glass envelope with all external parts being constructed of a non-oxidizable material. The lamp includes a conventional light-transmissive tubular ceramic body closed at its ends by ceramic end discs having refractory metal exhaust and fill tubulations extending therethrough which carry the discharge sustaining electrodes at their inner ends. A ceramic end chamber is sealed to the outside of the end discs and encloses the outwardly extending ends of the refractory metal tubulation. A plurality of platinum foil conductors are sealed through the juncture of the end chamber and its associated end disc with the inwardly extending ends of the platinum foil conductors electrically connected to the tubulation and their outwardly extending ends electrically connected to the lamp lead-in conductors.

United States Patent [191 Liberman et al'.

[ CERAMIC DISCHARGE LAMP OPERABLE IN AIR WITHOUT AN OUTER GLASS ENVELOPE [75] Inventors: Irving Liberman, Wilkinsburg;

' Robert J. Zollweg, Monroeville;

Walter J. Burnham, Pittsburg, all of Pa.

[73] Assignees Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Mar. 8, 1973 [21] Appl. No.: 339,490

[52] US. Cl 313/217, 313/218, 313/220,

. 313/221 [51] Int. Cl....- H0lj 61/36 [58] Field of Search 313/217-221 1 [56] References Cited UNITED STATES PATENTS 2,971,110 2/1961 Schmidt 313/221 3,609,437 9/1971 Tol et a1. 313/220 3,716,744 2/1973 Delembre et a1. 313/220 E 1I 20 Q 28 ---i:-':-

[ June 28., 1974 Primary Examiner-Herman Karl Saalbach Assistant Examiner-Siegfri'ed H. Grimm Attorney, Agent, or Firm-B. R. Studebaker [5 7] ABSTRACT A ceramic discharge lamp operable in air without a conventional sealed outer glass envelope with all external parts being constructed of a non-oxidizable material. The lamp includes a conventional lighttransmissive tubular ceramic body closed at its ends by ceramic end discs having refractory metal exhaust and fill tubulations extending therethrough which carry the discharge sustaining electrodes at their inner ends. A ceramic end chamber is sealed to the outside of the end discs and encloses the outwardly extending ends of the refractory metal tubulation. A plurality of platinum foil conductors are sealed through the junc-' ture of the end chamber and its associated end disc with the inwardly extending ends of the platinum foil conductors electrically connected to the tubulation and their outwardly extending ends electrically con-" nected to the lamp lead-in conductors.

9 Clains, 2 Drawing Figures CERAMIC DISCHARGE LAMP OPERABLE IN AIR WITHOUT AN OUTER GLASS ENVELOPE BACKGROUND OF THE INVENTION The ceramic discharge lamp employing the polycrystalline alumina or sapphire arc tube body has essentially revolutionized inner city street lighting and to some extent roadway lighting. With its ability to contain a sodium discharge and its associated high lumen output, major cities now evidence a bright orange-gold at night which approaches daylight lighting levels. The ceramic arc tube and its associated structure has in the past always been contained in an outer, lighttransmissive, generally vitreous envelope which is utilized to maintain the operative portion of the lamp in a vacuum or in a protective atmosphere of, for example an inert gas, to prevent oxidation of refractory metal leads and minimize any other deleterious effects which the high temperatures exhibited by the arc tube may have on its associated structures. Typical examples of the use of the ceramic arc tube conventionally disposed in an outer glass envelope can be found in US. Pat. No 3,623,134 to L. C. Werner et al and US. Pat. No. 3,363,134 to P. D. Johnson.

The use of an outer envelope of the type commercially available and that disclosed in the foregoing patents obviously provides a comparatively bulky package as compared to the size of the arc tube which alone provides the light output. Additionally, the sapphire or polycrystalline alumina (PCA) arc tubes have extensive possibilities for use as infrared sources in the 4 to 6 micron region where the alumina transmits readily but where outer envelopes of glass or quartz are generally highly absorbing. Another drawback to the outer envelope is in the area of optical laser pumping where more efficient radiation transfer between the pumping arc tube and the laser rod can be accomplished in the absence of the bulky outer envelope. In this connection, also a lamp without an outer jacket or envelope is more efficient since the outer jacket prevents efficient imaging and creates reflection losses in the laser pumping applications.

The reduced overall size of an air operated ceramic arc tube in the form of a self-contained lamp also has distinct possibilities in commercial applications where the size of the light source and its location with respect to reflectors and refractors can be critical in terms of light distribution and light applications.

charge lamps and more particularly to an arc discharge lamp wherein the ceramic arc tube represents the exterior body of the lamp. I-Ieretofore the ceramic arc tube has always been enclosed in an outer envelope because of the requirements for high-temperature refractory metals to withstand the temperature as electrode supports and lead-in conductors. These high-temperature refractory metal parts being readily oxidizable in air would lead to extremely early failure of the lamp if operated in air.

In accordance with the present invention an air operable ceramic discharge lamp is provided which is operable in air without an outer glass envelope and includes a light-transmitting tubular ceramic body, disc-shaped ceramic end closure means sealed to the ends of the tubular ceramic body with relatively rigid electrode support members sealed through the end closure means and carrying discharge sustaining electrodes on the innermost ends thereof. At least one of the electrode support members being a hollow tube to facilitate the exhausting and filling of the arc tube. A tubular ceramic chamber is sealed to the ceramic end closure means and encloses the outer ends of the relatively rigid electrode support members. Non-oxidizing, preferably platinum, electrical conductors are electrically connected to the relatively rigid electrode support members and extend through the seal area between the ceramic chamber and the ceramic end closure to the outside of the chamber.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to the drawing, wherein like reference characters represent like parts throughout the several views there is illustrated in FIG. 1 the air operable ceramic discharge lamp of this invention generally designated 10. The lamp 10 includes a lighttransmissive tubular ceramic body member 12 preferably of polycrystalline alumina or sapphire. The tubular ceramic body member or are tube 12 may be closed off at each end by having a ceramic disc 14 sealed to the end thereof at 16. The sealing composition employed to seal the end closure disc 14 to the arc tube body 12 must necessarily have a similar coefficient of thermal expansion as the ceramic parts joined thereby and must also beable to withstand attack from the alkali metal vapors employed in the discharge. A high melting point ceramic sealant such as a yttria-alumina or calciaalumina-silica sealing composition is preferred. Sealed to and extending through a central-aperture in the ceramic end closure discs 14 are tubular electrode support members 18 which may be of a refractory metal such as molybdenum, niobium or tantalum tubulation. Supported at their inner ends are the electrodes 20 which may be tungsten or activated tungsten electrodes with or without emissive material embedded therein. Again, the Y O -AI O or CAO-Al O -SiO sealing frits may be employed to secure the tubulation in the end closure disc.

A plurality of non'oxidizing foil electrical conductors 22 preferably of platinum are electrically connected to the tubulation 18 either by wrapping with refractory metal wire 24 or the foil conductors 22 may be welded directly to the refractory metal tubulation. A single foil conductor is also possible but more than one is preferred. The other ends of the foil lead-in conductors 22 overlie the outer edge of the end closure discs 14. A ceramic chamber 25 including a tubular portion 26 and an end cap 28 are sealed to the backside or outside of the ceramic end disc 14. The ceramic chamber may of course be constructed from sapphire or polycrystalline alumina but a high purity alumina ceramic is sufficient for purposes of the end chamber. As will be apparent, the foil conductors 22 are sealed between the inner edge of the end chamber 25 and the outside surface of the end disc 14 and the seal therebetween may be accomplished by any of the conventional lower temperature sealing compositions as for example a calciaalumina frit if the higher melting point Y O -A1 O is used at 16. The only caution being that the sealing composition employed at locations 30 have a lower melting point than the sealing composition employed at 16 inorder that the seals at 16 do not melt or decompose when the end chamber is sealed to the outside surface of the end closure discs.

The foil lead-in conductors 22 are electrically connected at their ends to lamp lead-in conductors 32 which may be any of stainless steel, platinum, nickel or nichrome by bands 34 which may also be any of the foregoing metals. Additional lead-in conductor support bands 38 for retaining the lead-in conductor 32 adjacent the side wall of the ceramic chamber 25 may also be employed.

In manufacturing the lamp of this invention, a conventional arc tube is fabricated which includes the sapphire or polycrystalline alumina body member 12 and the alumina end discs containing the molybdenum, niobium or tantalum tubulations inserted therein along with their associated tungsten electrodes. These parts are hermetically sealed in one vacuum firing operation using one of the relatively high melting point ceramic sealants, preferably the Y+ ,O -A1 O frit. The lamp is then filled as desired with a discharge sustaining filling as for example sodium, potassium other discharge sus-' taining alkali metal. One exampleof an operative lamp constructed in accordance with this invention was operated at 8 amps and 75 volts having a standard Vs inch O.D. polycrystalline alumina arc tube, an arc length of 2% inches with a lamp fill of 7 milligrams of potassium and 50 Torr of argon. After the arc tube or lamp is filled with a suitable discharge sustaining fill, the tubulation is pinch sealed in a conventional manner as at 40. As illustrated in the preferred embodiment, only the tubulation at one'end needs to include a pinch seal in the tubulation with the electrode supporting refractory metal tubulation at the other end being pre-formed with a closed end. Obviously, the electrode support at one end could be merely a solid rod.

The platinum lead-in conductors 22 are then secured to the tubulation 18 by either refractory metal wire 24 or by welding. Ceramic chambers 25 are then added through a separate firing operation, one end at a time, so that the other end can be kept relatively cool. In this way, the lamp fill will not create excessively high pressure which could open a seal or explode the lamp. If desired, a getter material, such as zirconium or yttrium may be placed inside the end chamber during the sealing operation in order that residual gasses trapped in the end cap will be gettered out rather than being permitted to react with the tubulation which could in some instances cause decreased life or even result in oxygen or hydrogen diffusing into the lamp body.

The final lamp will consist of components exposed to air which will not oxidize at temperatures up to and even beyond their melting points. The lowest melting point material in the lamp is the seal material, i.e. Ca0- A1 O employed to seal the end chamber 25 to the ceramic end disc 14. In principle, this sealant can be chosen to melt at a temperature slightly lower than the melting point of platinum (1774C).

As will be apparent from the foregoing, the lamp of this invention is characterized by a slim pencil-like configuration unencumbered by a heavy and bulky outer glass jacket, radiations beyond the infrared cutoff caused by quartz or glass outer bodies can be effectively utilized in this lamp, and the lamp can be better used in imaging applications such as laser pumping where bulky jackets prevent efficient imaging and create reflection losses. A lamp, constructed in accordance with this invention, will also run cooler than a jacketed lamp at the same wattage levels and should therefore inherently have longer life.

What is claimed is:

1. An air operable ceramic discharge lamp comprisa light transmissive ceramic body member;

a pair of body member end closure discs, one side of each of said discs being sealed to the ends of said body member to provide a discharge chamber;

refractory metal tubulation sealed through said body member end closure discs and extending both inwardly into said discharge chamberand away from said discharge chamber;

' opposed arc sustaining electrodes connected to the inwardly extending ends of said tubulation;

a ceramic chamber sealed to the other side of each of said body member end closure discs and surrounding the end of said tubulation extending away from said discharge chamber; and

non-oxidizing conductor means extending from outside each of said chambers through the seal area between said chamber and said end closure disc and electrically connected to the tubulation surrounded by said chamber.

2. An air operable ceramic discharge lamp according to claim 1 wherein said light-transmissive ceramic body is polycrystalline alumina and said non-oxidizing conductors are platinum.

3. An air operable ceramic discharge lamp according to claim 1 wherein said light-transmissive ceramic body member is sapphire and said pair of body member end closure discs are polycrystalline alumina.

4. An air operable ceramic discharge lamp according to claim 3 wherein said refractory metal tubulation is niobium and said opposed arc sustaining electrodes are tungsten.

5. A ceramic discharge lamp operable in air without an outer glass envelope, said ceramic discharge lamp comprising:

a light transmissive, tubular ceramic body;

disc-shaped ceramic end closure means sealed to the ends of said tubular ceramic body;

relatively rigid electrode support members sealed through said end closure means and carrying discharge sus'taining electrodes on the innermost ends thereof, at least one of said electrode support members being a hollow tube;

a tubular ceramic chamber sealed to said ceramic end clsoure means and enclosing the other ends of said relatively rigid electrode support members; and

non-oxidizing electrical conductor means electrically connected to said relatively rigid electrode support members and extending through a seal area to the outside of said chamber 8. A ceramic discharge lamp according to claim 7 wherein said non-oxidizing lead-in conductors are nickel and said non-oxidizing electrical conductor means is platinum.

9. A ceramic discharge lamp according to claim 5 wherein said relatively rigid electrode support member is niobium and said tubular ceramic chamber sealed thereabout is high-purity alumina. 

2. An air operable ceramic discharge lamp according to claim 1 wherein said light-transmissive ceramic body is polycrystalline alumina and said non-oxidizing conductors are platinum.
 3. An air operable ceramic discharge lamp according to claim 1 wherein said light-transmissive ceramic body member is sapphire and said pair of body member end closure discs are polycrystalline alumina.
 4. An air operable ceramic discharge lamp according to claim 3 wherein said refractory metal tubulation is niobium and said opposed arc sustaining electrodes are tungsten.
 5. A ceramic discharge lamp operable in air without an outer glass envelope, said ceramic discharge lamp comprising: a light transmissive, tubular ceramic body; disc-shaped ceramic end closure means sealed to the ends of said tubular ceramic body; relatively rigid electrode support members sealed through said end closure means and carrying discharge sustaining electrodes on the innermost ends thereof, at least one of said electrode support members being a hollow tube; a tubular ceramic chamber sealed to said ceramic end clsoure means and enclosing the other ends of said relatively rigid electrode support members; and non-oxidizing electrical conductor means electrically connected to said relatively rigid electrode support members and extending through a seal area to the outside of said chamber
 6. A ceramic discharge lamp according to claim 5 wherein said light-transmitting tubular ceramic body is polycrystalline alumina and said tubular ceramic chamber is high-purity alumina.
 7. A ceramic discharge lamp according to claim 5 wherein non-oxidizing lead-in conductors are electrically connected to said non-oxidizing electrical conductor means extending through said seal area to the outside of said chamber.
 8. A ceramic discharge lamp according to claim 7 wherein said non-oxidizing lead-in conductors are nickel and said non-oxidizing electrical conductor means is platinum.
 9. A ceramic discharge lamp according to claim 5 wherein said relatively rigid electrode support member is niobium and said tubular ceramic chamber sealed thereabout is high-purity alumina. 